Recently, there have been test broadcasts of a high definition television (HDTV) signal format which is capable of producing high quality television images. In view of the popularity of existing NTSC television systems and the large installed base of such equipment, television receivers which are capable of receiving image signals in both the NTSC and HDTV system formats are being made commercially available. Such television receivers employ one of two types of cathode ray tube (CRT) in which the aspect ratio of the screen surface is either 16:9 (representative of the HDTV format) or 4:3 (representative of the NTSC format). These television receivers contain a convertor for converting from one type of format to the other.
In the case where a television receiver has the screen with the aspect ratio of 4:3 for the NTSC format, an HDTV to NTSC system convertor (which enables reception of HDTV broadcasts on a standard NTSC television receiver) is used for displaying HDTV images on the screen of such television receiver. Such a display screen is illustrated in FIG. 1. As shown in FIG. 1, the image 91 in the HDTV system is displayed in the center section 92 occupying 3/4 (i.e., 9/12) of the height of screen 90. At the same time, the top and bottom sections 93 and 94 in screen 90 are rendered non-graphic or unusable for the display of picture information, so that these sections 93 and 94 are tinged black.
However, in the case of a television receiver of the HDTV system having the screen with the aspect ratio of 16:9, insertions of black images into the right and left sections in the screen and an addition of scanning lines are performed for displaying NTSC images with the aspect ratio of 4:3 on such screen. FIG. 2 is an illustration of a display screen in such a situation. The image 96 in the NTSC system is displayed in the center section 97 occupying 3/4 (i.e., 12/16) of the length of screen 95. At the same time, the left and right sections 98 and 99 in screen 95 are rendered non-graphic or unusable for the display of picture information, so that these sections 98 and 99 are tinged black.
In addition to television receivers which use a CRT, there are presently known in the art television receivers which use a liquid crystal display device instead of a CRT. Moreover, recently, projection-type television receivers have been developed in order to provide large-screen viewing. Such a projection-type television receiver uses a plurality of liquid crystal panels each capable of modulating a colored light being incident thereon. Each of these panels is supplied with, and driven by, image data for modulating the colored light and for producing an image light to be projected onto a screen.
Therefore, there is a need to render the above two types of television receivers, which use a liquid crystal display device, capable of displaying images in both the HDTV and NTSC system formats. Specifically, what is needed is the development of a driving apparatus and method for the liquid crystal display device to selectively display images with both the aspect ratios of 16:9 and 4:3 without unseemly viewing.